There is utilized a storage device having an encryption function in order to protect security of data. The storage device having the encryption function encrypts data by using an encryption key to preserve to a memory device. If the encryption key vanishes, the encrypted data cannot be decrypted, and therefore, the data practically vanishes as a matter of fact. On the other hand, it is not preferable from a view point of security to store the encryption key and the data encrypted by using the encryption key to the storage device. Because if a total of the storage device is stolen, the encrypted data is decrypted, and there is a concern of leaking information.
Hence, there is proposed a technology in which an encryption key is stored to a management server which is physically different from a storage device, and the storage device acquires to use the encryption key from the management server when it is needed (PTL 1).